Complex hydrides of the Group III-A metals are well known as having particularly effective properties as strong reducing agents and for starting materials in the preparation of other organic metallic compounds. For example, British Patent 757,524 describes the treatment of bimetal hydrides with an olefin to produce an alkyl bimetal compound, such as tetrapropyl lithium aluminum. Heretofore, however, these materials were necessarily made by rather complex and roundabout methods which, further, were wasteful of basic raw materials. Thus, Schlesinger and Finbolt, in U.S. Pat. No. 2,567,972 describe the preparation of materials such as lithium aluminum hydride, LiAlH.sub.4, by the reaction of an aluminum halide with either an alkali metal or an alkaline earth metal hydride in the presence of an aliphatic ether. A typical equation illustrative of this process is:
______________________________________ 4 LiH + AlCl.sub.3 .fwdarw. LiAlH.sub.4 + 3 LiCl lithium aluminum lithium lithium hydride chloride aluminum chloride tetrahydride ______________________________________
It is seen, readily, that in the above type of reaction the aluminum providing material is necessarily a halogen compound, and secondly, the halogen content thereof is not utilized. Further, the lithium hydride employed is very inefficiently utilized, viz., even at full effectiveness of the quoted reaction only one-fourth of the lithium appears in the desired product. Thus, the Schlesinger et al process is inherently very inefficient with respect to the alkali metal employed.
U.S. Pat. No. 3,556,740, issued Jan. 19, 1971 to Murib discloses a method for preparation of complex metal hydrides of the formula RXH.sub.4 wherein R is an alkali metal and X is a metal from the group consisting of aluminum, gallium, indium, and thallium which comprises hydrogenating a metal from the aforesaid group in the presence of an alkali metal hydride and an ether solvent for the complex metal hydride such as tetrahydrofuran (THF) or dimethyl ether of diethylene glycol (DMC).
The preparation of complex metal hydrides (MAlH.sub.4) in ether solvents has many disadvantages. The commercial grade ethers must be purified to completely remove water, alcohols and explosive peroxides and hydroperoxides before use. Long-term storage of ether results in deterioration of the complex metal hydrides due to ether cleavage and formation of unwanted alkoxy products. It is costly and fairly difficult to isolate solvent-free complex metal hydrides from ether solutions of these materials. Ether-type solvents such as tetrahydrofuran and dimethyl ether of diethylene glycol are high cost materials and are potentially dangerous in this type reaction if subjected to excessively high reaction temperatures. A violent explosion occurred in 1953 at Callery Chemical Company, Callery, Pa. when lithium aluminum hydride was being used to dry diethylene glycol dimethyl ether. The explosion was reported in Chemical and Engineering News, Vol. 31, p. 2334 (1953).
An object of the present invention is, then, to provide a new and more efficient process of producing the complex hydride compounds of certain Group III-A metals with electropositive metals of the alkali and alkaline earth types. A more particular object is to provide such a process which achieves a substantially improved utilization of raw materials. A further object is to provide a process for making such complex bimetal hydrides directly from low priced raw materials. An additional object of certain forms of the process of the invention is to provide a direct route and an accelerated or catalyzed technique for effecting the process. Other objects will appear thereafter.